1. Field of the Invention
The present invention relates to an apparatus for generating power from a mechanical energy of a rolling tire and a system for monitoring a physical parameter of the tire using the apparatus.
2. Description of the Related Art
Systems currently in practical use for monitoring physical parameters of tires, such as a tire pressure monitoring system (TPMS) that monitors a pressure of a rolling tire and passes the pressure information to the driver in real time, uses a button battery as the power source. The button batteries, however, cause problems that they limit applicable wheel shapes depending on the size thereof and require time and money for each replacement since they have a limited operating life. Further, the battery provides power by chemical reaction and poses a problem of power instability in the interior of a tire where temperature variation is very large.
In order to solve these problems, tire monitoring systems that do not use batteries and, instead, make use of vibrations of rolling tires for power generation and vibration power generators for use with the systems have been studied. For example, International Patent Publication No. WO2003/095244 discloses a self-powered tire assembly having a patch of piezoelectric material for generating an electric charge from a mechanical strain developed in a tire. The document also describes that silica, barium titanate, cadmium sulfide, zirconate titanate (PZT), polyvinylidene fluoride, polyvinyl chloride (PVC) are preferably used as the piezoelectric material. U.S. Pat. No. 7,415,874 discloses an electrical energy generation system having a power source of piezoelectric device linked to a tread area of a tire, in which PZT is used as the material of the piezoelectric device.
Non-lead piezoelectric materials among the piezoelectric materials described in the patent documents other than PZT, however, has low piezoelectric performance and unable to provide sufficient power. In contrast, PZT provides markedly superior piezoelectric performance in comparison with other materials, but it contains highly poisonous Pb, which may leak out from waste products in the manufacturing process, from materials in use, or from those discarded after use, thereby causing environmental problems, including soil pollution, air pollution, and the like.
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide a non-lead interior tire power generation apparatus having high power generation capability and a tire monitoring system using the apparatus.